The viscosity of diesel fuel is sensitive to the temperature of the diesel fuel, such that it is desirable that the fuel reaching the engine is neither overly cold nor overly hot. The prior art has disclosed various methods for achieving improved engine performance by managing the temperature of the diesel fuel supplied to the engine. In one modern solution, diesel fuel that is returning from the engine is routed directly to the fuel pump so that the benefit of heat transferred into the fuel within the engine compartment is retained. This is achieved by a thermostatic valve installed in the fuel return line. When the returning fuel is below a certain threshold temperature the fuel is directed directly to the fuel pump for immediate return to the engine. However, after the fuel temperature reaches an upper threshold, the thermostatic valve will dump the returning fuel into the fuel reservoir so that the heated fuel will become mixed with the larger volume of fuel held in the reservoir. In this way, the engine can be supplied with relatively warmer fuel during engine warm-up and yet the fuel will not be overheated to the detriment of engine performance.
It would be desirable to improve the afore described thermostatic valve to prevent the possibility of returning overly heated fuel to the engine by assuring that the overly heated fuel will be dumped in the reservoir.